Myeloperoxidase-antineutrophil Cytoplasmic Antibodies (MPO-ANCA) and Proteinase 3-ANCA without Immunofluorescent ANCA Found by Routine Clinical Testing

A challenging case of granulomatosis with polyangiitis with cardiac involvement: a rare case report

Background

Granulomatosis with polyangiitis (GPA), a systemic antineutrophil cytoplasmic antibody (ANCA) associated vasculitis, is characterized by inflammation of the small arteries, arterioles, and capillaries classically manifesting with glomerulonephritis and necrotizing granulomatous lesions of the upper and lower respiratory tract. With an incidence of approximately 12 cases per one million individuals per year it is an uncommon diagnosis that typically presents as frequent pulmonary and sinus infections; however, if left without definitive treatment progresses to more severe manifestations specifically hemoptysis and hematuria.

Case Description

This case report highlights a 15-year-old woman who had both classic and non-classic findings making the diagnosis challenging. Specifically, her age of presentation, improvement with anti-microbials, and coronary dilation were not classic. Additionally, her lab work was negative for the cytoplasmic subset antineutrophil cytoplasmic autoantibody (c-ANCA), but positive for serum anti-proteinase 3 antineutrophil cytoplasmic antibody (PR3-ANCA) which further delayed the ultimate diagnosis as this is typically c-ANCA positive.

Conclusions

Other systemic vasculitides, such as mucocutaneous lymph node disease, are associated with cardiac pathology necessitating further medical management and follow-up to prevent increased morbidity and mortality. Knowing this, we conclude that further evaluation for cardiac pathology would be prudent as part of the initial workup of patients with a diagnosis of GPA. Included is a brief review of available literature on GPA to emphasize the typical presentation, lab findings, and importance of early diagnosis.

Performance of MPO-ANCA and PR3-ANCA immunoassays for the stratification of specific ANCA-associated vasculitis: A systematic review and meta-analysis

OBJECTIVE

To determine the impact of myeloperoxidase (MPO) and proteinase 3 (PR3) antigen-specific immunoassays in the stratification of patients at-risk for anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitides (AAV) at diagnosis.

METHODS

A Medline search was conducted to identify diagnostic accuracy studies using PR3-ANCA or MPO-ANCA for the evaluation of granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Studies estimates were pooled using the bivariate method.

RESULTS

Diagnostic accuracy varied by analyte and AAV subtype. PR3-ANCA had greater sensitivity than MPO-ANCA for GPA (74% vs 11%, p < 0.001) and MPO-ANCA greater sensitivity for MPA (73% vs 7%, p < 0.001). Specificities of both MPO-ANCA and PR3-ANCA were consistently high (mean 97%, range: 93-99%) for both AAV subtypes. There was insufficient data to perform meta-analysis for the diagnostic accuracy of EPGA.

CONCLUSION

These results validate the use of high quality MPO-ANCA and PR3-ANCA immunoassays to screen patients at-risk for AAV as well as to categorize disease as GPA or MPA subtype. However, caution must be exercised in doing so, since some assays may not have optimal performance. Each laboratory should validate appropriate algorithms based on the tests used and testing population.

A Comparative Evaluation of Antigen-Specific Sandwich Immunoassay and Indirect Immunofluorescence Assay (IIF) in Detecting Antineutrophil Cytoplasmic Antibodies: Are We Ready to Replace IIF with ELISA as the Primary Screening Method?

Background Antineutrophil cytoplasmic antibodies (ANCA) are important biomarkers in the diagnosis of ANCA-associated vasculitis, and indirect immunofluorescence (IIF) had been the method of choice for its detection from the very beginning. However, international consensus on ANCA testing (2017) advocates the use of high-quality immunoassays as the primary screening method. The purpose of this study was to evaluate the diagnostic performance of enzyme-linked immunosorbent assay (ELISA) compared to IIF in detecting ANCA.

Methods One-hundred eighty-nine serum samples of suspected or known cases of systemic vasculitis were screened for ANCA by IIF and proteinase-3- and myeloperoxidase-ELISA. In IIF, positive results were further divided into cytoplasmic pattern of ANCA and perinuclear pattern of ANCA, depending upon the pattern of fluorescence. McNemar’s chi-squared test was applied to check the equality of proportions of positive results, and Kappa statistics was used to measure the agreement between the two methods. Diagnostic performance of ELISA was evaluated taking IIF as reference.

Results IIF detected ANCA in 17.5% cases and ELISA detected it in 11.6% cases. A good agreement between the overall performance of ELISA and IIF was observed ( K -value: 6.8, p -value: < 001). However, a significant difference in the proportion of positive results by the two methods was observed in McNemar’s test (two-sided p -value: 0.007). Taking IIF as standard, ELISA showed 60.6% sensitivity, 98.7% specificity, and predictive value of positive and negative results of 90.9 and 92.2%, respectively.

Conclusion The new generation antigen-specific ELISAs had high specificity but the chances of missing cases in primary screening due to the low sensitivity and high false negativity (39.4%) need to be dealt with.

In vitro diagnostics for the medical dermatologist. Part I: Autoimmune tests

Despite the expansion of available in vitro laboratory tests at a rate far exceeding that of dermatologic pharmaceuticals, the existing literature is dominated by discussion of the latter. With the advent of numerous new tests, it can be difficult for practicing dermatologists to stay up-to-date on the available options, methodologies, and recommendations for when to order one test over another. Understanding the inherent strengths and weaknesses of these options is necessary to inform appropriate ordering and proper interpretation of the results. The first article in this continuing medical education series summarizes information on methodology, test characteristics, and limitations of several in vitro laboratory tests used for the work up of undifferentiated patients suspected of having dermatologic autoimmune diseases and it provides a general guide to ordering these tests.

The value of anti-neutrophil cytoplasmic antibodies (ANCA) testing for the diagnosis of ANCA-associated vasculitis, a systematic review and meta-analysis

The testing of anti-neutrophil cytoplasmic antibodies (ANCA) takes an important place in the diagnostic workup to ANCA-associated vasculitis (AAV). Nowadays, it is recommended to screen for the presence of PR3 and MPO specific antibodies first using immunoassay, without the need for ANCA measurement by indirect immunofluorescence (IIF). A literature search was performed to assess the diagnostic test value of ANCA IIF and PR3- and MPO-antibody immunoassay to diagnose AAV. This meta-analysis shows that the c-ANCA testing by IIF has a pooled sensitivity of 75.2% and a pooled specificity of 98.4%. For PR3-antibody immunoassay, the pooled sensitivity depended on the immunoassay method used, and ranged from 79.8% to 86.6%, whereas the pooled specificity ranged from 96.8% to 98.3%. For both p-ANCA IIF and MPO-antibody immunoassay (all methods) sensitivity varied considerably showing pooled values of respectively 46.3% and 58.1%, whereas respective pooled specificity was 91.4% and 95.6%. These findings support the 2017 international consensus that primary anti-PR3 and anti-MPO screening by immunoassay, based on superior immunoassay sensitivity without the need for IIF ANCA testing, improves the diagnostic workup of AAV.

The performance of the chemiluminescent immunoassay for measuring serum myeloperoxidase and proteinase 3 antibodies

Background

Enzyme‐linked immunosorbent assay (ELISA) has traditionally been used to detect myeloperoxidase (MPO) and proteinase 3 (PR3) antibodies, although it is time‐consuming and physically demanding. As a novel and highly effective immunoassay, we compared chemiluminescent immunoassay (CIA) with ELISA to verify the application value of CIA in MPO and PR3 antibodies detection.

Methods

By ELISA and CIA, serum levels of anti‐MPO and anti‐PR3 antibodies were measured in 63 anti‐neutrophil cytoplasmic antibody (ANCA)‐associated vasculitis (AAV) patients (AAV group), including 47 microscopic polyangiitis (MPA) patients and 16 granulomatosis with polyangiitis (GPA) patients, in addition, 68 patients in interference control group (IC group), 19 healthy subjects in healthy control group (HC group). We compared MPO and PR3 antibodies levels and positive rates measured by these two methods among groups. Relationship and coincidence rate between ELISA and CIA were investigated. Diagnostic values for clinical outcomes for MPO and PR3 antibodies were assessed by receiver operator characteristic (ROC) curve.

Results

In AAV patients, when detecting anti‐MPO (r = .90) and anti‐PR3 (r = .81), CIA was highly correlated with ELISA, companying with highly total (88.89%, 92.06%, respectively) and positive coincidence rates (84.78%, 77.27%, respectively). In HC group, anti‐PR3 positive rate detected by both immunoassay were 0, anti‐MPO almost were 0, which without statistically significant difference (P = .32). In IC group, the total (76.47%, 58.82, respectively) and positive coincidence rates (48.38%, 30.00%, respectively) of anti‐MPO and anti‐PR3 were the lowest, but the negative coincidence rates reached 100%. By CIA, similar to ELISA, the levels of anti‐MPO were significantly higher both in AAV patients (56.00; [4.40‐235.30]) and MPA patients (98.00; [27.90‐324.70]) compared with either IC group (3.20; [3.20‐18.55) (P < .0001) or HC group (3.20; [3.20‐3.20]) (P < .0001), yielded an area under curve (AUC) of 0.76 for AAV and 0.89 for MPA, the concentration of anti‐PR3 in GPA group (66.65; [24.43‐150.00]) was significantly higher than that in IC group (2.3; [2.3‐10.95]) (P < .0001) and HC group (2.3; [2.3‐2.3]) (P < .0001), with an AUC of 0.92.

Conclusion

Similar to ELISA, CIA was competent to detect MPO and PR3 antibodies in AAV patients and healthy population, thus distinguish AAV patients from IC group and HC group and effectively diagnose MPA and GPA.

A Case Report of Multiple Myeloma Associated With Myeloperoxidase and Proteinase-3 Antibodies Posing a Diagnostic Dilemma

Multiple myeloma (MM) is a clonal proliferation of antibody-producing plasma cells that can precipitate renal injury through multiple mechanisms. Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is an inflammatory condition that can result in renal failure through mononuclear cell infiltration and consequent destruction of glomeruli. Several case reports have identified clinical situations where differentiating these entities has been challenging. Renal biopsy is an invaluable tool in differentiating between MM and AAV when clinical uncertainty exists. We report the case of an 85-year-old man who presented with a rapid decline in renal function and serologies positive for both MM and AAV. Renal biopsy findings confirmed the diagnosis of myeloma kidney and excluded vasculitis. This case highlights an unusual clinical scenario in which both proteinase-3 (PR-3) and myeloperoxidase (MPO) antibodies are positive. While these antibodies are both individually associated with ANCA vasculitis, they are seldom simultaneously positive. Our case would suggest that positive PR-3 and MPO antibodies should raise concern for an alternative diagnosis. Indeed, ANCA, PR-3, and MPO antibodies can all be positive in patients with monoclonal gammopathy in the absence of vasculitis. Our case underscores the value of renal biopsy in the setting of MM.

Bartonella Endocarditis Mimicking Crescentic Glomerulonephritis with PR3-ANCA Positivity

Bartonella henselae is a fastidious organism that causes cat scratch disease, commonly associated with fever and lymphadenopathy but, in rare instances, also results in culture-negative infectious endocarditis. We describe a patient who presented with flank pain, splenic infarct, and acute kidney injury with an active urinary sediment, initially suspicious for vasculitis, which was subsequently diagnosed as B. henselae endocarditis. Bartonella endocarditis may present with a crescentic glomerulonephritis (GN) and elevated PR3-ANCA antibody titers, mimicking ANCA-associated GN, with 54 cases reported in the literature. Unique to our case in this series is a positive PR3-ANCA antibody despite a negative IIF-ANCA. Thus, the presentation of Bartonella can mimic ANCA-associated GN, and renal biopsy showing immune complex deposition is critical for diagnosis and appropriate treatment.

Chemiluminescent immunoassay technology: what does it change in autoantibody detection?

Diagnostic technology is rapidly evolving, and over the last decade, substantial progress has been made even for the identification of antibodies, increasingly approaching this type of diagnostic to that of automated clinical chemistry laboratory. In this review, we describe the analytical and diagnostic characteristics of chemiluminescence technology in its strength and in its applicability for a more rapid and accurate diagnosis of autoimmune diseases. The wide dynamic range, greater than that of immunoenzymatic methods, the high sensitivity and specificity of the results expressed in quantitative form, the high degree of automation and the clinical implications related to the reduction in the turnaround time, and the ability to run a large number of antibody tests (even of different isotypes), directed towards large antigenic panels in random access mode, make this technology the most advanced in the clinical laboratory, with enormous repercussions on the workflow and on the autoimmunology laboratory organisation. Further improvements are expected in the coming years with the development of new analytical platforms such as the flow-injection chemiluminescent immunoassay, the two-dimensional resolution for chemiluminescence multiplex immunoassay and the magnetic nanoparticles chemiluminescence immunoassay, which will likely result in additional increases in the clinical efficacy of antibody tests.

Pathology of Antineutrophil Cytoplasmic Antibody–Associated Pulmonary and Renal Disease

Context.—Antineutrophil cytoplasmic antibody (ANCA)–associated vasculitis commonly presents with pulmonary and renal involvement that may present diagnostic challenges.

Objectives.—To highlight the updates in the classification of small vessel vasculitis, present the patterns of pulmonary and renal pathology in which ANCA-associated vasculitis is included in the differential diagnosis, analyze the screening and specific antineutrophil cytoplasmic antibody testing methods in the clinical laboratory, compare and contrast the 3 major ANCA-associated vasculitis diseases, and review the pathophysiologic mechanisms of tissue injury in this setting.

Data Sources.—Data are derived from published literature and clinical experience.

Conclusions.—Although rare, ANCA-associated vasculitis diseases are often considered in the differential diagnosis of many pathologic patterns of pulmonary and renal disease. Histopathologic diagnosis of specific entities in this context nearly always requires correlation of the pathology with clinical and serologic data.